In the present patent application, the term “coating material” is used to designate any material in liquid or in powder form that is to be sprayed towards an article to be coated, e.g. a primer, a paint, or a varnish.
U.S. Pat. No. 4,776,520 describes a rotary atomizer for spraying liquid paint. That rotary atomizer has a body comprising a main inner portion and an outer portion fastened to the inner portion, by screw-fastening. The rotary atomizer of U.S. Pat. No. 4,776,520 also has an atomizer member for atomizing the coating material, and a turbine. The atomizer member is arranged at a downstream end of the body in such a manner as to form a spray of paint, when said atomizer member is driven in rotation by the turbine. Outlet channels are provided in the body, uniformly about the axis of rotation. The function of the outlet channels is to eject air so as to shape the spray of paint, these jets of air usually being referred to as “shroud air”. The rotary atomizer also has an outlet chamber that is formed in the body and that extends about the axis of rotation. The outlet chamber communicates with each outlet channel. Upstream from the outlet chamber, an inlet duct is provided in the body so as to feed compressed air to the outlet chamber and thus to the outlet channels.
It is observed that the flow rates of shroud air flowing through the respective outlet channels are not distributed uniformly about the axis of rotation. A single inlet duct brings air into the annular outlet chamber. That annular outlet chamber generates head losses that increase with increasing distance from the inlet duct. That non-uniform distribution of the flow rates of air might, if it is not controlled, cause undesired asymmetry in the spray of coating material, and thus in the thickness of the layer of coating material deposited on the article to be coated, in particular while the rotary atomizer is moving facing the article to be coated.
A particular object of the invention is to remedy those drawbacks, by proposing a rotary atomizer that achieves controlled distribution, e.g. uniform and symmetrical distribution, of the shroud air about the spraying axis, with limited air consumption.